1. Field of the Invention
The present invention relates to chemical mechanical planarization (CMP) techniques and, more particularly, to the efficient, cost effective, and improved CMP operations.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then, metal CMP operations are performed to remove excess material.
A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material or polyurethane in conjunction with other materials such as, for example a stainless steel belt. In operation, the belt pad is put in motion and then a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A shows a linear polishing apparatus 10 which is typically utilized in a CMP system. The linear polishing apparatus 10 polishes away materials on a surface of a semiconductor wafer 16. The material being removed may be a substrate material of the wafer 16 or one or more layers formed on the wafer 16. Such a layer typically includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer 16 to planarize a surface layer of the wafer 16.
The linear polishing apparatus 10 utilizes a polishing belt 12, which moves linearly in respect to the surface of the wafer 16. The belt 12 is a continuous belt rotating about rollers (or spindles) 20. The rollers are typically driven by a motor so that the rotational motion of the rollers 20 causes the polishing belt 12 to be driven in a linear motion 22 with respect to the wafer 16.
The wafer 16 is held by a wafer carrier 18. The wafer 16 is typically held in position by mechanical retaining ring and/or by vacuum. The wafer carrier positions the wafer atop the polishing belt 12 so that the surface of the wafer 16 comes in contact with a polishing surface of the polishing belt 12.
FIG. 1B shows a side view of the linear polishing apparatus 10. As discussed above in reference to FIG. 1A, the wafer carrier 18 holds the wafer 16 in position over the polishing belt 12 while applying pressure to the polishing belt. The polishing belt 12 is a continuous belt typically made up of a polymer material such as, for example, the IC 1000 made by Rodel, Inc. layered upon a supporting layer. The polishing belt 12 is rotated by the rollers 20 which drives the polishing belt in the linear motion 22 with respect to the wafer 16. In one example, a fluid bearing platen 24 supports a section of the polishing belt under the region where the wafer 16 is applied. The platen 24 can then be used to apply fluid against the under surface of the supporting layer. The applied fluid thus forms a fluid bearing that creates a polishing pressure on the underside of the polishing belt 12 which is applied against the surface of the wafer 16. Unfortunately, because the polishing pressure produced by the fluid bearing typically cannot be controlled very well, the polishing pressure applied by the fluid bearing to different parts of the wafer 16 generally cannot be separately managed. Therefore, prior art fluid bearings generally do not accurately control wafer polishing on the leading and trailing edges of the wafer 16.
FIG. 1C shows a linear polishing apparatus 10 illustrating leading edge and trailing edge polishing pad deformations. In this example, a wafer 16 is attached to a carrier 18 and the carrier 18 by use of pressure 13 pushes the wafer 16 down on the polishing belt 12 that is moving in the direction 23 over the platen 24. When the wafer contacts the polishing belt 12, the polishing belt 12 deforms at a leading edge 16a and at a trailing edge 16b. A deformation 22 occurs at the leading edge 16a and a deformation 26 occurs at trailing edge 16b. The deformation 16a generally causes more polishing pressure on the leading edge 16a resulting in more material being removed. The deformation 16b generally causes less polishing pressure on the trailing edge 16b resulting in less material being removed. Consequently, due to the fact that the prior art polishing belt designs do not properly control polishing dynamics, uneven polishing and inconsistent wafer polishing may result thereby decreasing wafer yield and increasing wafer costs.
Therefore, there is a need for an apparatus that overcomes the problems of the prior art by having a platen that improves polishing pressure control and reduces polishing pad deformation.
Broadly speaking, the present invention fills these needs by providing an apparatus for independently controlling the leading edge and the trailing edge of a wafer during CMP. The method involves utilizing an improved fluid bearing platen with strategically utilized fluid ports to powerfully control fluid pressure pushing on certain regions of the polishing pad. In this way, polishing pressure in different sections of a wafer may be separately controlled as well as polishing pad deformation during polishing. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a platen assembly for supporting an underside of a linear polishing pad is disclosed. The platen assembly includes a platen surround plate, a platen interface assembly, and a platen manifold assembly. The platen manifold assembly is connected to the platen interface assembly, and the platen manifold assembly is supported by the platen surround plate. The platen manifold assembly includes a base plate, a gasket that fits on the base plate, an o-ring fitting around the platen, and a platen. The platen includes a plurality of separately controllable regions where each of the separately controllable regions is designed to communicate independent fluid flows through the separately controllable regions to the underside of the linear polishing pad.
In yet another embodiment, a platen for mounting under and supporting a linear polishing pad during chemical mechanical planarization (CMP) operations is disclosed. The platen includes a plate that has a plurality of separately controllable regions where each of the separately controllable regions is designed to communicate independent fluid flows through the separately controllable regions to the underside of the linear polishing pad.
In another embodiment, a platen for mounting under and supporting a linear polishing pad during chemical mechanical planarization (CMP) operations is provided. The platen is designed to apply a force to the underside of the linear polishing pad as a wafer is applied to a top surface of the polishing pad. The wafer is applied substantially over the platen so as to define the linear polishing pad between the wafer and the platen. The platen includes a plate having a plurality of output holes where each of the output holes designed to output an fluid flow. The plurality of output holes is separately grouped so as to define a first region and a second region of output holes. The first region is oriented substantially under a leading edge of the wafer and the second region is oriented substantially under the trailing edge of the wafer. The first region of output holes and the second region of output holes is separately controlled so as to apply a different magnitude of the force to the leading edge of the wafer than the trailing edge of the wafer.
The advantages of the present invention are numerous. Most notably, by creating a platen that can fine tune and adjust polishing pressure in the edges of the wafer and reduce deformation of a polishing pad during polishing, wafers produced may be made more uniform which may result in greater wafer yields and lower wafer costs. Specifically, the present invention may independently manage polishing pressures in the leading edge and the trailing edge of the wafer and reduce deformity of the polishing pad as it enters underneath the wafer and exits from underneath the wafer during polishing in a linear belt polishing unit. Such control may be established by individually controlling fluid pressure applied by different zones of a platen to the polishing pad moving over the platen. In addition, the present invention may have even more specific control over polishing pressures within each of the different zones by enabling more precise fluid pressure control within different sub regions of each zone of the platen. Therefore, control of fluid pressure may be controlled even more precisely to optimize fluid pressure applied to the polishing pad. This may result in more controllable polishing pressure on different parts of the polishing pad thereby enabling reduction of deformity of the polishing pad. Consequently, great differences in polishing pressures in different regions of the wafer may be significantly reduced.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.